Zarys struktury facjalnej miocenu zatoki rzeszowskiej (Polskie Karpaty Wschodnie)

Abstract

AN OUTLINE OF FACIES STRUCTURE OF THE MIOCENE IN THE RZESZÓW EMBAYMENT Summary Shallow-water Lithothamnium rocks (limestones, sandstones, conglomerates, mudstones, marls, and claystones) from margins of the Rzeszów Embayment (Figs. 1, 2) were assigned to the Opole (Moravy) member by W. Friedberg (2) and J. Gołąb (4). On the basis of paleontological and geological analysis of my collections of fossils from classic and new outcrops, I differentiated the Lithothamnium Opolian (Przylasek, Niechoborz, Olimpów, Tyczyn, and Hermanowa localities) with a new faunistic record (13, 14, 15, 16), and Lithothamnium Grabovian (Babica locality), hitherto unidentified in the Carpathian region (8, 9, 10, 11, 14, 17, 18, 19, 20, 21). In the Lithotamnium Limestones from Babica I also found the Spiratella-Radiolaria-Globigerina assemblage (cooccurring with plant-easting species of bivalves and gastropods, representing marine environment with brackish features), indicative of the Chodenice member developed in the Lithothamnium facies (J. Urbaniak, "Southern Lithothamnium zone of the Badenian - the Polish Carpathians and Carpathian Foredeep" and „Littoral Lithothamnium interstratofacies in the Badenian of the Skole Carpathians - the Rzeszów Lithothamnium center" - papers delivered at the scientific meeting of the Commission of Geological Sciences, Cracow Branch of the Polish Academy of Sciences, Cracow, 1985.06.26). The strata mentioned above represent Opolian-Grabovian monolith, with features of Badenian interstratigraphic biolithofacies and faunistic connections with Badenian Lithothamnium strata of the Carpathian region, Holy Cross Mts, Lublin-Roztocze area, and Ukraine and Wien region (17, 19, 20). I regard the Lithothamnium facies zone of the Badenian as related to a intrabasinal threshold, Carpathian-Miocene swell (Skole Flysch and Lower Miocene) with tectonic-geomorphological foundations (Fig. 3). The threshold acted as a divide of the Opolian-Grabovian basin of the Carpathian "flange" (6) into a closed, southern zone and open-sea (neritic-bathyal) northern. Both zones are represented by pelitic sediments and deep-water fauna: pteropod-Orbulinid-pecten in the Opolian, and turritellid-buliminid one in the Grabovian. The age of strata, bathymetry, and character of the S-N paleorelief of the Opolian-Grabovian basin of the Rzeszów Carpathian are defined by characteristic assemblages and species of Opolian and Grabovian marine faunas (see Polish text and Fig. 3). The faunas indicate depths down to 100 m or even 200 m in the zone of the Lithothamnium sedimentation, and below 1000 m in the northern and southern zones of the basin. The paleorelief of the Opolian basin in the Carpathians is interpreted as a stratigraphic horst of the Grabowiec structure, characterized by increased bathymetric contrast in the Rzeszów Embayment and unstable paleogeomorphology, reflected by the Pobitno and Mogielnica basins, Brzozowa- Gromnik basin (furrow) basin and other forms. The Lithothamnium strata of the Rzeszów Embayment are not directly related to southern margin of the Carpathian land but rather to an intrabasinal threshold of Carpathian basement (island archipelago, cordillera) and they form a barrier of the reef type (Fig. 3). Analysis of faunas of the Carpathian Miocene showed existence of a few latitudinally oriented intrabasinal thresholds, beneath the Carpathians (Opolian) and above them (Opolian and Grabovian - 19). Sedimentation developing in the zone of these threshold was littoral, reef-Lithothamnium in character, and unrelated to the Carpathian land. Macrofaunal assemblages (comprising bivalves, gastropods, pteropods, plankton, and representatives of other systematic groups) appear usable as the major criterion in reconstructing the Carpathian Miocene basin. The assemblages are especially sensitive indicators of marine environment and the reconstructions should be based on results of ecological and sedimentological analyses (mode of deposition of fossils, origin of organic and inorganic components of sediment, alimentary areas).